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Zinc Complexes of Amino Acids and Peptides, 7 . Solution Behavior and Zinc Complexation of Dipeptides Made up Solely from Histidine and Cysteine
Author(s) -
Gockel Peter,
Vogler Raphael,
Vahrenkamp Heinrich
Publication year - 1996
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19961290803
Subject(s) - chemistry , zinc , histidine , perchlorate , peptide , cysteine , iodide , amino acid , chloride , imidazole , medicinal chemistry , stereochemistry , inorganic chemistry , polymer chemistry , organic chemistry , ion , biochemistry , enzyme
The eight possible types of dipeptides made up from histidine and cysteine, namely the unprotected ones H‐His‐Cys‐ OH ( 1 ) and H‐Cys‐His‐OH ( 2 ), the N ‐protected ones Ac‐His‐Cys‐OH ( 3 ) and Ac‐Cys‐His‐OH ( 4 ), the C ‐protected ones H‐His‐Cys‐OEt ( 5 ) and H‐Cys‐His‐NH 2 ( 6 ), and the fully protected ones Ac‐His‐Cys‐OEt ( 7 ) and Ac‐Cys‐His‐OEt ( 8 ) were prepared analytically pure. Their acid‐base behavior and zinc complexation in solution were studied potentiometrically. In all cases 1:1 (zinc:peptide) complexes are the dominant species near neutral pH. 1:2 complexes could only be detected for 4, 6, 7 , and 8 , and precipitations occurred in basic media. From equimolar mixtures of the peptides and zinc salts (chloride, iodide, perchlorate) solid complexes were obtained upon addition of a base. They always contain coordinating anions (chloride, iodide, or trifluoroacetate which was introduced with the peptide). They have the composition LZnX for L = 5‐8 and L 4 Zn 5 X 2 for L = 1–4 . It is proposed that all complex species observed contain tetrahedral zinc, that they are monomers in dilute solution and thiolate‐bridged oligomers in the solid state, and that the peptides as a rule occupy at least three coordination sites.